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Brushless DC Servo Driver K-Cube
maximum, in the range 0% to 100%. When the accumulated energy exceeds the value
specified in the
Energy Limit
parameter, a 'current foldback' condition is said to exist, and
the commanded current is limited to the value specified in the
Current Limit
parameter.
When this occurs, the Current Foldback status bit (bit 25) is set in the Status Register and
the ‘Current Limit’ LED on the GUI panel is lit. When the accumulated energy above the
Current Limit
value falls to 0, the limit is removed and the status bit is cleared.
Motor Limit
– This parameter sets a limit for the motor drive signal and accepts values in
the range 0 to 100% (32767). If the system produces a value greater than the limit set,
the motor command takes the limiting value. For example, if the
Motor Limit
is set to
30000 (91.6%), then signals greater than 30000 will be output as 30000 and values less
than -30000 will be output as -30000.
Motor Bias
– When an axis is subject to a constant external force in one direction
(such as a vertical axis pulled downwards by gravity) the servo filter can compensate
by adding a constant DC bias to the output. This bias is set in the
Motor Bias
parameter, which accepts values in the range -32768 to 32767. The default value is
0. Once set, the motor bias is applied while the position loop is enabled.
Tracking & Settling Settings
Moves are generated by an internal profile generator, and are based on either a
trapezoidal or s-curve trajectory (see Section 6.3.3.). A move is considered complete
when the profile generator has completed the calculated move and the axis has
'settled' at the demanded position.
The system incorporates a monitoring function, which continuously indicates whether
or not the axis has 'settled'. The 'Settled' indicator is bit 14 in the Status Register and
is set when the associated axis is settled. Note that the status bit is controlled by the
processor, and cannot be set or cleared manually.
The axis is considered to be 'settled' when the following conditions are met:
• the axis is at rest (i.e. not performing a move),
• the error between the demanded position and the actual motor position is less than or
equal to the specified number of encoder counts (0 to 65535) set in the
Settle Window
field,
• the above two conditions have been met for a specified number of cycles
(1 cycle = 102.4 µs), set in the
Settle Time
field (range 0 to 32767).
The above settings are particularly important when performing a sequence of moves.
If the PID parameters (see Section 6.3.3.) are set such that the settle window cannot
be reached, the first move in the sequence will never complete, and the sequence will
stall. The settle window and settle time values should be specified carefully, based on
the required positional accuracy of the application. If positional accuracy is not a
major concern, the settle time should be set to '0'. In this case, a move will complete
when the motion calculated by the profile generator is completed, irrespective of the
actual position attained, and the settle parameters described above will be ignored.
The processor also provides a 'tracking window' which is used to monitor servo
performance outside the context of motion error. The tracking window is a
programmable position error limit within which the axis must remain, but unlike the
